Python’s Collections Module: Counter

Python Collections Module (9 Part Series)

1 Python’s Collections Module: Introduction
2 Python’s Collections Module: Counter
… 5 more parts…
3 Python’s Collections Module: Why dictionaries maintain insertion order but printing Counter doesn’t?
4 Python’s Collections Module: OrderedCounter
5 Python’s Collections Module: OrderdDict
6 Python’s Collections Module: defaultdict
7 Python’s Collections Module: namedtuple
8 Python’s Collections Module: deque
9 Python Collections: Hackerrank Question on Counter

Introduction

A Counter is a dict subclass for counting hashable objects → any object which is not mutable.

It is a collection where elements are stored as dictionary keys and their counts are stored as dictionary values.

#To use it, ofcourse we need to first import it from collections import Counter

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Using Counter

myList = ['k', 'k', 1, 1, 2, 2, 1, 2, 3, 3, 1, 'a']
myString = "CodeBlooded"

# simply pass any iterable # Counter(iterable) returns a Counter obj count1 = Counter(myList)
count2 = Counter(myString)

#How does a Counter obj look? print(count1, count2, sep='\n')

"""Output Counter({1: 4, 2: 3, 'k': 2, 3: 2, 'a': 1}) Counter({'o': 3, 'd': 3, 'e': 2, 'C': 1, 'B': 1, 'l': 1}) """" 

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As counter is a subclass of dictionary, it has all the methods of the dictionary.

most_common(n) method

The most_common(n) returns a list of n most common objects along with their respective counts.

from collections import Counter

myList = ['k', 'k', 1, 1, 2, 2, 1, 2, 3, 3, 1, 'a']
myString = "CodeBlooded"

# simply pass any iterable # Counter(iterable) returns a Counter object count1 = Counter(myList)
count2 = Counter(myString)


print(count1, count2, sep='\n')

# If n is omitted or None, most_common() # returns all elements in the counter. print(count1.most_common(2))
print(count2.most_common(3))

"""Output Counter({1: 4, 2: 3, 'k': 2, 3: 2, 'a': 1}) Counter({'o': 3, 'd': 3, 'e': 2, 'C': 1, 'B': 1, 'l': 1}) [(1, 4), (2, 3)] [('o', 3), ('d', 3), ('e', 2)] """

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Common Patterns with Counter

For a given Counter object c,

Feel free to fire up your ipython or python shell and try this commands out for better understanding 🙂

Let’s wrap up this post with a problem where Counter is very helpful.

Finding most frequent word using Counter in a given string

from collections import Counter

string = "string with repeated word Jello So what is Jello Who cares what is Jello anyways but Jello must be repeated Jello number of Jello times"

# You can use re.split() for more complex patterns! words = string.split()
words_count = Counter(words)
print("Most Occurring word is",
      words_count.most_common(1))

"""Output Most Occurring word is [('Jello', 6)] """

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if you notice, while printing the Counter object – it doesn’t maintain the order of elements present in the iterable passed. Do you know why?

Try googling or duckduckgoing! I will answer this question in next post

Python Collections Module (9 Part Series)

1 Python’s Collections Module: Introduction
2 Python’s Collections Module: Counter
… 5 more parts…
3 Python’s Collections Module: Why dictionaries maintain insertion order but printing Counter doesn’t?
4 Python’s Collections Module: OrderedCounter
5 Python’s Collections Module: OrderdDict
6 Python’s Collections Module: defaultdict
7 Python’s Collections Module: namedtuple
8 Python’s Collections Module: deque
9 Python Collections: Hackerrank Question on Counter

原文链接：Python’s Collections Module: Counter